DENVER--Two rivers in Colorado and New Mexico hit hardest by toxic waste spilled from a defunct gold mine will remain closed to drinking water and irrigation intakes for at least another week, but test samples show a gradual ebbing of contamination, environmental officials said on Tuesday. The San Juan River and its northern tributary, the Animas River, have been fouled by the release of more than 3 million gallons (11.3 million liters) of acid mine drainage inadvertently triggered by a team of Environmental Protection Agency workers last Wednesday. The discharge has continued to flow at the rate of about 500 gallons (1,900 liters) a minute from the site of the century-old Gold King Mine, near the town of Silverton in southwestern Colorado, into a stream below called Cement Creek. From there, the wastewater has washed into the Animas River and into the San Juan River in northwestern New Mexico. Some residents who live downstream from the mine and draw their drinking supplies from private wells have reported water discoloration, but there has been no immediate evidence of harm to humans, livestock or wildlife, according to EPA officials. Still, residents were advised to avoid drinking or bathing in well water, and the government was supplying water where needed. Two Colorado municipalities, including Durango, and the New Mexico towns of Aztec and Farmington have shut off their river intakes. The bright orange contamination plume, containing heavy metals such as arsenic, mercury and lead, has dissipated through dilution as the discharge spreads downstream, with its leading edge no longer visible from aerial surveys, the EPA said "As it moves on, we are seeing a downward trajectory toward pre-event conditions," EPA chief Gina McCarthy said at a clean-energy event in Washington. The Animas River in Durango, about 50 miles (80 km) south of the spill, had turned from orange to bright lime green by Sunday, and was a darker shade of blue-green by Tuesday, a sign that pollutants were gradually clearing, at least near the surface, said Sinjin Eberle, a spokesman for the conservation group American Rivers. But experts said a long-term concern was the deposit of heavy metals from the spill that had settled into river sediments, where they can be churned up and unleash a new wave of pollution when storms hit or rivers run at flood stage.